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As the acknowledged leader in server virtualisation VMware is well aware of the pretenders snapping at its heels. Virtualisation remains a hot topic and it is becoming an increasingly crowded market, with a range of offerings, some commercial and some coming from the open source community. One very obvious response to this from VMware has been to offer a number of free packages in addition to its core commercial products. Of these free packages, VMware Server is the one that has the potential to make the biggest splash.

VMware Server is, as suggested by its name, a complete server virtualisation package. It enables a user to install it on a server box and then to use it to create a number of virtual machines. These virtual machines (called guest systems) run as processes on the main box (the host system), and from within they appear to be running on a real box, complete with processor, memory, peripherals, network connectivity and so on. In this way it's possible for one physical machine to be running multiple operating systems concurrently. Each virtual machine is isolated from the others and from the host, so that it can be stopped, started, reconfigured and put to work as required. Each virtual machine can have one or more virtual hard disks, which in reality are files on the host system but appear as complete partitioned disks on the guest.

Note that while the product is labelled VMware Server, it is not strictly necessary to install it on a physical machine running a server operating system. On a Windows system it's perfectly feasible to run VMware Server on XP Professional or Windows 2000 Pro, for example. And, unlike a number of other virtualisation products, VMware Server is remarkably flexible in the range of operating systems that can be installed as guests, from multiple versions of Windows, different flavours of Linux, Solaris and even Novell Netware.

Installation is straightforward, it's just a case of downloading the install files to the host and clicking through the installer. Once installed it's possible to go ahead and create the virtual machines as guests. This is also a straightforward process that involves selecting which operating system it's going to run, creating the configuration of the machine (how much memory, which virtual drives, peripherals etc). The next stage is to do the install, which means launching the virtual machine in a window and watching it go through the BIOS boot screen and then look for the install disks to begin the same kind of install process that you'd go through to install a real machine.

Each virtual machine can be set up with a range of networking options, from appearing on the network like a real machine to networking with the host only to being completely isolated.

So far all of the basic functionality described matches that in VMware's key Workstation product. However there are some key differences. Firstly this is a server product and it's geared to creating guests systems used for production loads. Guests can be set up to load when the host machine boots up, to be safely shut down when the host does and to run in the background when the host is running. The console application which is the main interface can be used to switch between guests and to operate on them. When the console is closed the guests carry on running in the background.

The Workstation product is much more geared to developers, sys admins and tech support people. It allows users to create multiple snapshots of guest systems, has more in the way of debugging support and so on.

However, there's no denying that for many users VMware Server is more than enough functionality. For example while it doesn't allow for multiple snapshots, it does allow the creation of a snapshot of a guest system. This means you can create a snapshot of a system, apply a patch or install some new software and if it fails or causes problems you can revert to the snapshot and lose all of the changes that were made.

This is an impressive piece of software, and it's certainly much more powerful and feature rich than this quick review can hope to cover. It is very highly recommended.